1. Field of the Invention
The present invention relates to a data communication apparatus having an auto-dialing function.
2. Related Background Art
There is known a conventional facsimile apparatus that, in the case where the apparatus automatically effects image communication following an auto-dialing operation using an auto-dialing function, may need to set a pause period into the auto-dialing operation. The apparatus waits while the set pause period elapses after making a call to a destination, and the apparatus starts a procedure for image communication after the set pause period elapses.
FIG. 4 shows a sequence of the procedure when the pause period is set into the auto-dialing operation. The pause period is necessary for waiting for a telephone switching machine to connect a telephone line to the destination if the telephone switching machine spends a long time connecting the telephone line. In the case where the destination sends a message to the calling station in response to reception of a call, it is necessary that the pause period be set. One pause data P is set at the end of the telephone number, like setting the telephone number when the telephone number is registered into a one-touch dialing key (or an abbreviating dial key). The time corresponding to one pause data P is for example ten seconds. If a long pause period is necessary, plural pause data P may be set at the end of the telephone number, so that the pause period will be ten seconds times the number of pause data P. The apparatus discriminates if the pause data is set or not when the apparatus makes a call. If the pause data is set, the apparatus starts the procedure for image communication after the time corresponding to the set pause data has elapsed. In the procedure, the apparatus discriminates if a response signal is received from the destination or not while a fixed period T1 (i.e. thirty five seconds) elapses from starting the procedure. The fixed period T1 has been decided by the recommendation T30 defined by the CCITT (International Telephone & Telegraph Communication Committee).
If the response signal is not received during the fixed period the apparatus terminates the procedure for facsimile communication.
In the above described art, however, the telephone switching machine may connect the telephone line to the destination in a shorter time than the set pause period. Nevertheless, the apparatus always waits for the set pause period to elapse before it starts to effect the procedure and discriminate if the response signal is received or not. Therefore the start of image communication is delayed, as FIG. 5 shows.
As FIG. 6 shows, in the case where a longer pause period than the fixed period T1 is set into the auto-dialing operation and the telephone switching machine does not actually need such a long pause period to connect the telephone line to the destination, then the apparatus often terminates the procedure for image communication without completing the image communication. This is because the destination's facsimile apparatus starts its own procedure in response to receiving a call so that, when the apparatus (the calling side) starts its procedure and then waits too long in the pause period, the destination facsimile apparatus does not receive an expected signal and therefore terminates its procedure.